In a known type of rolling block firearm, the bolt is housed in the rolling block and has two tenons which project from the front of the block and which, when the block is closed, fit snugly into two mortises made in the receiver that supports the barrel (or barrels).
Turning the key towards the open position makes the bolt slide back towards the gun stock, thus disengaging the tenons from the mortises and causing them to move back into the rolling block.
The coupling between the key and the bolt is made by an eccentric tooth that fits into a socket made in one side of the bolt. This type of coupling requires of the gun user a relatively high critical release moment to overcome the friction between receiver and bolt when the latter is in the closed position.
To obtain an acceptable value for the critical release moment, firearm manufacturers, when designing a firearm, tend to reduce the overall coupling surface between mortises and tenons. This, however, causes unwanted slipping between the receiver and the bolt every time a shot is fired. This slipping causes wear on the mortises and tenons which, in the long run, leads to slack and vibrations. To compensate for the wear, the two tenons are made longer so that, when a gun is new, they do not enter the mortises completely and go in further and further over time, as they gradually wear.
Obviously, wear compensation of this type is possible until such time as the tenons go into the mortises as far as possible. Once this limit has been reached, the gun requires maintenance which is very expensive.
In addition to this drawback, compensation for wear as just described causes the closing position of the key to drift, eventually leading to its misalignment with respect to the line of sight and disturbing the shooter's aim. To avoid this, shoulder firearms are normally manufactured in such a way that the key in a new gun is shifted to the right of the line of sight and tends to come into line with it as the tenons and mortises wear.
The present invention has for an object to provide a device for opening and closing rolling block firearms that overcomes the above mentioned drawbacks.
According to the invention, this object is achieved by a device for opening and closing rolling block firearms having the characteristics described in claim 1.
The claims dependent on claim 1 refer to advantageous preferred embodiments of the invention.